This invention relates to mattresses, and more particularly to sleeper sofa mattresses of the type having an inner spring unit and an overlying top cushion. In conventional mattresses having inner spring units and top cushions, it has been known to secure the top cushion to the underlying inner spring through lines of transverse stitching. Such constructions are illustrated in U.S. Pat. Nos. 3,110,043 and 2,168,037. As illustrated in these patents, a narrow strip or flange may be secured to the inner face of the top cushion at the lines of transverse stitching and secured to the spring construction by suitable means, such as hog rings. As illustrated in these patents, two lines of transverse stitching typically divide the mattress into three sections providing extra support in the center one-third of the mattress where body weight is concentrated.
In contrast to conventional mattresses, sleeper sofa mattresses are designed to be foldable and extendable. Such mattresses may be extended to provide a flat sleeping surface and may be folded along transverse flexures for storage within the sofa. When folded, a part of the mattress may be doubled over, providing a flat surface for the placement of sofa seat cushions, and part of the mattress may be angled upwardly to fit within the back of the sofa. In many sleeper sofas, the head of the mattress and support frame are designed to be angled upwardly to provide a raised headrest for reading or television viewing. However, when the sleeper sofa mattress is of the type having an inner spring unit and an overlying top cushion, folding the mattress and raising the headrest may cause the top cushion to bunch and shift position. This bunching and shifting may make it more difficult to fold the mattress When the mattress is folded with the sofa, the bunching and shifting may reduce the sofa's seating comfort. And, over time, the bunching and shifting may shorten the useful life of the mattress.